First, are you trying to get the requisite response from the White House at 100,000 signatures in 30 days, it might have to go through petitions.whitehouse.gov. Not sure at all though.

Second, you probably don't want to advertise on the front page, because your ad targets a specific audience, and reddit is (in general) liberal, which isn't necessarily aligned with your cause. You could advertise on /r/MensRights, which would be a more targeted approach.

Third, instead of throwing money at it, I think partnering with various mens rights groups might be more effective.